Ball Racket

ABSTRACT

A ball racket includes a head frame for racket stringing, a shaft unit including first and second tubes non-rotatably fitted to each other to be moved relative to each other along an axis, an actuator disposed within the first tube and having an actuating end and a shank body, an expandable shell disposed between the actuating end and the first tube, and a force transmitting mechanism disposed between the expandable shell and the first tube. Counterclockwise rotation of the actuating end causes the expandable shell and thus the first tube to expand radially so as to generate increased friction between the first and second tubes to thereby guard against relative axial movement between the first and second tubes. Clockwise rotation of the actuating end permits the first tube to axially move relative to the second tube so as to adjust the length of the shaft unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a ball racket, more particularly to a ball racket having a telescopic shaft unit.

2. Description of the Related Art

A conventional tennis racket generally includes a head frame and a shaft extending from the head frame and having a grip portion. Since the distance between the head frame and the grip portion is fixed, e.g., 19″, 23″, 25″ and 27″, the shafts of tennis rackets have to be formed in various lengths to suit different users. Hence, a fast-growing teenager tennis player needs to buy new rackets with longer shafts from time to time.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a ball racket having a telescopic shaft unit whose length is adjustable to suit different users.

According to this invention, the ball racket includes a head frame adapted for racket stringing, a shaft unit, an actuator unit, an expandable shell, and a force transmitting mechanism. The shaft unit includes first and second tubes. The first tube has a first front end securely connected to the head frame, and a first tubular segment extending from the first front end along an axis to terminate at a first rear end. The second tube has a second front end and a second tubular segment which extends from the second front end along the axis to terminate at a second rear end. An inner tubular surface of the second tubular segment is configured to be frictionally engaged with and to be movable relative to an outer surrounding surface of the first tubular segment along the axis. The actuator unit has an actuating end which is disposed within the first tube and which is radially spaced apart from the inner surrounding surface by a surrounding gap, and a shank body which extends from the actuating end along the axis to terminate at an operated end that extends outwardly of the first rear end and that is operable manually to rotate the actuating end about the axis. The expandable shell is inserted into the surrounding gap, and has outer and inner shell surfaces respectively confronting the inner surrounding surface and the actuating end. The force transmitting mechanism is disposed between the inner shell surface and the actuating end such that, as a result of counterclockwise rotation of the actuating end about the axis, the expandable shell is forced to expand radially to an expanded position, where the outer surrounding surface is urged against the inner tubular surface by an urging force to result in an increased frictional force therebetween, thereby guarding against movement of the second tube relative to the first tube along the axis, and such that, as a result of clockwise rotation of the actuating end about the axis, the expandable shell is displaced to a contracted position, where the inner tubular surface is relieved of the urging force so as to be movable relative to the outer surrounding surface along the axis.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiment of the invention, with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of the preferred embodiment of a ball racket according to this invention;

FIG. 2 is an exploded perspective view of a shaft assembly of the ball racket of the preferred embodiment;

FIG. 3 is a fragmentary sectional view of the shaft assembly, illustrating an expandable shell therein in a contracted position;

FIG. 4 is a cross-sectional view of the shaft assembly taken along lines IV-IV of FIG. 3;

FIG. 5 is a view similar to FIG. 3, illustrating the expandable shell in an expanded position, and a first tube in an extended state; and

FIG. 6 is a cross-sectional view taken along lines VI-VI of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 to 3, the preferred embodiment of a ball racket according to the present invention is shown to comprise a head frame 10, a shaft unit 20, an actuator unit 50, an expandable shell 60, and a force transmitting mechanism.

The head frame 10 is adapted for racket stringing. The shaft unit 20 includes a first tube 30 and a second tube 40. The first tube 30 has a first front end 39 securely connected to the head frame 10, and a first tubular segment 31 extending from the first front end along an axis (X) to terminate at a first rear end 32. The first tubular segment 31 has inner and outer surrounding surfaces 33,35 radially opposite to each other. The inner surrounding surface 33 includes a first larger-diameter region 331 and a first smaller-diameter region 332 disposed adjacent to the first front end 39 and the first rear end 32, respectively. The first tubular segment 31 is punched radially and inwardly to form a pair of guard rail regions 34 on the inner surrounding surface 33, and a pair of corresponding keyway regions 36 in the outer surrounding surface 35. The second tube 40 has a second front end 49 and a second tubular segment 41 which extends from the second front end 49 along the axis (X) to terminate at a second rear end 42. The second tubular segment 41 has an inner tubular surface 43 which has a pair of keys 44 extending radially and inwardly therefrom and engaging slidably and respectively the keyway regions 36 so as to guide movement of the first tubular segment 31 relative to the second tubular segment 41 along the axis (X). The inner tubular surface 43 includes a second larger-diameter region 431 and a second smaller-diameter region 432 which are disposed adjacent to the second front end 49 and the second rear end 42, respectively. The second larger-diameter region 431 has a cross-section configured to mate with the outer surrounding surface 35 for facilitating movement of the second tube 40 relative to the first tube 30. The second tubular segment 41 further has an outer tubular surface 45 which is radially opposite to the inner tubular surface 43 and which is configured to be gripped by a player.

The actuator unit 50 has an actuating end 51 which is disposed within the first tube 30 and which is radially spaced apart from the first larger-diameter region 331 by a surrounding gap (A), and a shank body 54 which extends from the actuating end 51 along the axis (X) to terminate at an operated end 53 that extends outwardly of the first rear end 32 and through the second smaller-diameter region 432, and which is movable along the axis (X) through the first smaller-diameter region 332. A twistable knob 70 is disposed rearwardly of the second rear end 42, is coupled with the operated end 53 by means of a pin 80 that extends radially through an outer surrounding wall 72 and an inner tubular wall 73 of the twistable knob 70 and the operated end 53, and is operable manually to rotate the actuating end 51 about the axis (X). In addition, the actuator unit 50 further has a small-diameter portion 55 extending forwardly from the actuating end 51, and front and rear stoppers 56,57 which are respectively disposed forwardly of the small-diameter portion 55 and rearwardly of the actuating end 51.

The expandable shell 60 is inserted into the surrounding gap (A), and includes two shell halves 61 which respectively have inner surface regions 611 cooperatively serving as an inner shell surface that confronts the actuated end 51, and outer surface regions 612 cooperatively serving as an outer shell surface that confronts the inner surrounding surface 33 and that has a cross-section configured to mate with the first larger-diameter region 331, and a spring O-ring 62 which is fitted in engaging grooves 613 formed respectively in the outer surface regions 612 to be hooped on the outer surface regions 612 so as to bias the inner surface regions 611 toward the actuating end 51. Each of the shell halves 61 has groove segments 614 disposed in the outer surface region 612 thereof. The groove segments 614 of the shell halves 61 extend in an axial direction parallel to the axis (X) to cooperatively define a pair of guiding grooves 615. The guard rail regions 34 of the first tube 30 are configured to be fitted into the guiding grooves 615 in spline engagement.

The force transmitting mechanism includes internally and externally threaded portions 64,52 which are disposed respectively on the inner surface regions 611 and the actuating end 51, and which are threadedly engaged with each other. The externally threaded portion 52 has an outer diameter which is gradually increased toward the shank body 54.

As shown in FIGS. 5 and 6, when the actuator unit 50 is rotated about the axis (X) in a counterclockwise direction as indicated by arrow 100, the internally and externally threaded portions 64,52 are fully engaged with each other, the shell halves 61 are axially moved toward the rear stopper 57, and the outer surface regions 612 are displaced radially and outwardly against a biasing action of the spring O-ring 62 so as to permit displacement of the expandable shell 60 to an expanded position, where the outer surrounding surface 35 of the first tubular segment 31 is urged against the inner tubular surface 43 of the second tubular segment 41 by an urging force to result in an increased frictional force therebetween, thereby guarding against movement of the second tube 40 relative to the first tube 30 along the axis (X). The threaded movement of the expandable shell 60 toward the shank body 54 is limited by the rear stopper 57, as shown in FIG. 5.

As shown in FIGS. 3 and 4, when the actuator unit 50 is rotated about the axis (X) in a clockwise direction as indicated by arrow 200, the internally and externally threaded portions 64,52 are partially engaged with each other, and the outer surface regions 612 are displaced radially and inwardly by the biasing action of the spring O-ring 62 to decrease the frictional force between the outer surrounding surface 35 and the inner tubular surface 43 such that the expandable shell 60 is displaced to a contracted position, where the inner tubular surface 43 of the second tube 40 is relieved of the urging force so as to be movable relative to the outer surrounding surface 35 of the first tube 30 along the axis (X). The forward threaded movement of the expandable shell 60 is limited by the front stopper 56, as shown in FIG. 3. At this stage, the second tube 40 is movable along the axis (X) relative to the first tube 30 to permit adjustment of the length of the shaft unit 20 to suit different users. Moreover, the rear stopper 57 is dimensioned such that the rear stopper 57 is prevented from moving outwardly of the first smaller-diameter region 332.

While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this invention is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretations and equivalent arrangements. 

1. A ball racket comprising: a head frame adapted for racket stringing; a shaft unit including a first tube which has a first front end securely connected to said head frame, and a first tubular segment extending from said first front end along an axis to terminate at a first rear end, said first tubular segment having inner and outer surrounding surfaces radially opposite to each other, and a second tube having a second front end and a second tubular segment which extends from said second front end along the axis to terminate at a second rear end, said second tubular segment having an inner tubular surface which is configured to engage said outer surrounding surface with a frictional force and to be movable relative to said outer surrounding surface along the axis, and an outer tubular surface which is radially opposite to said inner tubular surface, and which is configured to be gripped by a player; an actuator unit having an actuating end which is disposed within said first tube and which is radially spaced apart from said inner surrounding surface by a surrounding gap, and a shank body which extends from said actuating end along the axis to terminate at an operated end that extends outwardly of said first rear end such that said operated end is operable manually to rotate said actuating end about the axis; an expandable shell which is inserted into said surrounding gap, and which has outer and inner shell surfaces that are radially opposite to each other, and that respectively confront said inner surrounding surface and said actuating end; and a force transmitting mechanism disposed between said inner shell surface and said actuating end such that, as a result of counterclockwise rotation of said actuating end about the axis, said expandable shell is forced to expand radially to an expanded position, where said outer surrounding surface is urged against said inner tubular surface by an urging force to result in an increased frictional force therebetween, thereby guarding against movement of said second tube relative to said first tube along the axis, and such that, as a result of clockwise rotation of said actuating end about the axis, said expandable shell is displaced to a contracted position, where said inner tubular surface is relieved of the urging force so as to be movable relative to said outer surrounding surface along the axis.
 2. The ball racket according to claim 1, wherein said force transmitting mechanism includes internally and externally threaded portions which are respectively disposed on said inner shell surface and said actuating end, which are threadedly engaged with each other, and which are configured such that the counterclockwise and clockwise rotation of said actuating end result in threaded movement of said internally threaded portion relative to said externally threaded portion to permit displacement of said expandable shell to the expanded and contracted positions, respectively.
 3. The ball racket according to claim 2, wherein said externally threaded portion has an outer diameter which is gradually increased toward said shank body such that the threaded movement of said internally threaded portion toward said shank body as a result of the counterclockwise rotation of said actuating end results in radial expansion of said expandable shell so as to permit displacement of said expandable shell to the expanded position.
 4. The ball racket according to claim 3, wherein said expandable shell includes two shell halves which respectively have inner surface regions cooperatively serving as said inner shell surface, and outer surface regions cooperatively serving as said outer shell surface, and a spring O-ring which is fitted on said outer surface regions so as to bias said inner surface regions toward said actuating end such that, as a result of the counterclockwise rotation of said actuating end, said internally and externally threaded portions are fully engaged with each other and said outer surface regions are displaced radially and outwardly against a biasing action of said spring O-ring so as to increase the frictional force, and such that, as a result of the clockwise rotation of said actuating end, said internally and externally threaded portions are partially engaged with each other and said outer surface regions are displaced radially and inwardly by the biasing action of said spring O-ring so as to decrease the frictional force.
 5. The ball racket according to claim 4, wherein said shell halves respectively have groove segments respectively disposed in said outer surface regions and extending in an axial direction parallel to the axis to cooperatively define a guiding groove, said first tubular segment being punched radially and inwardly to form a guard rail region on said inner surrounding surface, and a corresponding keyway region in said outer surrounding surface, said guard rail region being configured to be fitted in said guiding groove in spline engagement such that rotation of said actuating end results in axial movement of said expandable shell relative to said actuating end between the expanded and contracted positions.
 6. The ball racket according to claim 5, wherein said second tubular segment has a key extending radially and inwardly from said inner tubular surface and engaging slidably said keyway region so as to guide movement of said first tubular segment relative to said second tubular segment along the axis.
 7. The ball racket according to claim 4, wherein said inner surrounding surface includes a first larger-diameter region and a first smaller-diameter region which are disposed adjacent to said first front end and said first rear end, respectively, said first larger-diameter region having a cross-section configured to mate with a combined cross-section of said outer surface regions of said shell halves for facilitating axial movement of said shell halves within said first tube, said first smaller-diameter region being dimensioned to permit movement of said shank body along the axis.
 8. The ball racket according to claim 7, wherein said actuator unit has front and rear stoppers which are respectively disposed forwardly and rearwardly of said externally threaded portion and which are dimensioned to limit the threaded movement of said internally threaded portion relative to said externally threaded portion, said rear stopper being further dimensioned to be prevented from moving outwardly of said first smaller-diameter region.
 9. The ball racket according to claim 7, wherein said inner tubular surface includes a second larger-diameter region and a second smaller-diameter region which are disposed adjacent to said second front end and said second rear end, respectively, said second larger-diameter region having a cross-section configured to mate with said outer surrounding surface for facilitating movement of said second tube relative to said first tube, said second smaller-diameter region being dimensioned to permit extension of said operated end therethrough.
 10. The ball racket according to claim 9, further comprising a twistable knob which is disposed rearwardly of said second rear end and which is coupled with said operated end so as to be operable manually to rotate said actuating end. 